Control device for eliminating malfunctions in a network

ABSTRACT

Electrical malfunctions in a network which are caused by torque fluctuations of an electric motor, in particular flicker, are reduced by using a control device. For simple and cost-effective minimizing or even correction of such malfunctions with the control device, the control device has at least one first input for supplying an input signal which contains information suitable for determining the loading of the network by torque fluctuations and at least one output for transmitting an output signal to at least one converter supplying the electric motor. This makes it possible to reduce or ideally to eliminate electrical malfunctions in a network which are caused by torque fluctuation of the electric motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of International ApplicationNo. PCT/EP2013/059585, filed May 8, 2013, which designated the UnitedStates and has been published as International Publication No. WO2013/182368 and which claims priority of German Patent Application,Serial No. 10 2012 209 369.9, filed Jun. 4, 2012, pursuant to 35 U.S.C.119(a)-(d).

BACKGROUND OF THE INVENTION

The invention relates to a control device for reducing electricalmalfunctions in a network which are caused by torque fluctuations of anelectric motor, in particular flicker. The invention also relates to asystem having a control device of this type and to a method for reducingelectrical malfunctions which are caused by torque fluctuations of anelectric motor, in particular flicker, in a network by means of acontrol device of this type.

One cause of malfunctions, for example flicker, in a network is torquefluctuations in drive devices which are electrically connected to thenetwork. In a drive device, an electric motor which is supplied via aconverter is coupled to a mechanical load or a mechanical source.Malfunctions can arise when the mechanical load, for example a pistoncompressor, or the mechanical source, such as an internal combustionengine has a varying torque pattern. This leads to variations in thenetwork current which can then cause malfunctions in the network. Theelectric motor can be operated either as a motor, so that it convertselectrical energy into mechanical energy in order thereby to drive aload, or it can be operated as a generator when it converts mechanicalenergy into electrical energy in order thereby to generate electricalenergy. The converter serves to control the energy flow. A convertercontrol system is associated with the converter, inter alia, forreceiving target value signals. It can be arranged in the immediatevicinity of, particularly in a common switchgear cabinet together with,the converter or spatially separate therefrom. An uneven mechanicalloading on the motor shaft, which is caused, for example, by theoperation of a piston compressor, leads to an uneven electrical loadingon the network, which can manifest itself in the form of networkmalfunctions such as flicker. The uneven mechanical loading of theelectrical motor can be buffered and reduced in that a large inertialmass is used on the motor shaft. This reduces the interfering effects onthe electrical side of the electric motor. However, the inertial massincreases the structural volume, the weight and thus also the costs ofthe motor unit, sometimes even significantly.

It is an object of the invention to minimize and ideally to eliminate,by simple and inexpensive means, electrical malfunctions arising fromtorque fluctuations during operation of a load or a source at anelectric motor which is electrically supplied by means of a converterconnected to the network.

SUMMARY OF THE INVENTION

This object is achieved by means of a control device for reducingelectrical malfunctions in a network which are caused by torquefluctuations of at least one electric motor, in particular flicker,wherein the control device comprises at least one first input forsupplying an input signal which contains information suitable fordetermining the loading of the network by torque fluctuations and atleast one output for outputting an output signal to at least oneconverter supplying the electric motor to reduce the electricalmalfunctions in the network caused by torque fluctuations of theelectric motor.

This object is further solved by a system having at least one electricmotor, a converter supplying the at least one electric motor, and atleast one control device for reducing electrical malfunctions in anetwork caused by torque fluctuations of the at least one electricmotor, wherein the control device includes at least one first input forsupplying an input signal with information suitable for determiningloading of the network by torque fluctuations, and at least one outputfor outputting an output signal to at least one converter supplying theelectric motor for reducing the electrical malfunctions in the networkcaused by the torque fluctuations of the electric motor, and by a methodfor eliminating electrical malfunctions in a network with a controldevice, wherein the method includes receiving with a controller of thecontrol device at least one first input signal which comprisesinformation suitable for determining loading of the network by torquefluctuations associated with at least one electric motor, generatingwith the controller from the at least one first input signal at leastone output signal, and transmitting the at least one output signal to aconverter supplying the at least one electric motor.

The invention is based on the recognition that malfunctions in thenetwork can be minimized or even eliminated through the processing ofinformation regarding the loading of the network by torque fluctuations,by surprisingly simple means.

The control device intervenes in the interplay of mechanical energy andelectrical energy, wherein the converter acts as the actuating elementin this arrangement. For this purpose, the control device receivessuitable information on the loading of the network as the inputvariable. In order to counteract this loading of the network, dependingon the input signal, a corresponding output signal is generated and istransferred to the converter as the actuating element. The mainadvantage of a control system of this type is that inertial masses canbe dispensed with or at least reduced. Aside from a reduced weight andreduced costs, in this way, at the same time, a large dynamic range ofthe drive can be achieved.

Advantageous developments of the invention are disclosed in thedependent claims.

In an advantageous embodiment, the input signal contains information onthe electric power absorbed by or fed in by the at least one electricmotor from the network or on the currents and/or voltages applied to theelectric motor. These variables are particularly well suited fordetermining the loading of the network through torque fluctuations. Thedetermination can be carried out, for example, by means of calculationsor estimations. One advantage of these variables is that these can bemade available relatively simply with suitable measuring devices. Thisembodiment is particularly advantageous if corresponding measuringdevices are already present in the system for other regulation, controlor monitoring tasks, so that the relevant variables can be easily fed tothe control device.

In a further advantageous embodiment, the control device has at leastone further input for supplying a further input signal which containsmechanical information derived from the electric motor, in particularregarding the rotary speed and/or the rotor angle. From thisinformation, a relationship between the loading on the network and therotor angle can be obtained. This relationship can be used to make theregulation operate in a frequency-selective manner. This has the greatadvantage, inter alia, that the adjustment dynamics are used for thefrequency components with which action can be most effectively takenagainst the malfunction.

In a further advantageous embodiment, the regulating system has meansfor frequency analysis provided for processing the input signals. Thishas the great advantage, inter alia, that the adjustment dynamics areused for those frequency components with which action can be mosteffectively taken against the malfunction.

In a further advantageous embodiment, the output signal containsinformation on the target torque and/or on the voltages of theconverter. The advantage of this embodiment is that the control devicecan easily be connected to the converter control system since theconverter control system often has an input for a torque target value.The advantage of the voltage outputs lies in the formation of differentexisting regulating circuits separately in order to be able also tooptimize them separately. For this purpose, for example, a rotary speedregulation uses the input of the converter control system for the torquetarget value, whereas the control device for reducing malfunctions inthe network acts upon the voltages of the converter. Thus a separationof the regulating tasks is possible and the individual tasks can each beoptimized separately.

In another advantageous embodiment, the system has a motor regulator forrectifying malfunctions in the network. The advantage of thisarrangement is that existing regulating systems with motor regulators,for example, with the aim of regulating the rotary speed, can also beenhanced with a control device according to the invention in order torectify malfunctions caused by the torque fluctuations. This enhancementwith a control device in order to eliminate malfunctions can possiblyalso take place retrospectively.

In another advantageous embodiment, the system has a coupling unit forcoupling the output signal of the control device and the output signalof the motor regulator. The advantage of this embodiment is that thecontrol device is integrated as simply as possible into a correspondingsystem, possibly also into an existing system. Existing outputs of amotor controller are coupled by simple means to the outputs of thecontrol device via the coupling unit, in order to feed these outputs tothe converter control system. Particularly for retrospectiveenhancements of the system with a control device for reducingmalfunctions in the network, by this means, simple integration isenabled. With this enhancement, the converter control system does notneed to be extended with further inputs.

In a further advantageous embodiment, a high-pass filter is used forfiltering the input signal of the electrical power. This ensures, interalia, that changes to a rotary speed target value are not interpreted bythe controller as a malfunction. In this way, the interaction ofdifferent control circuits is prevented as far as possible. Furthermore,low-frequency components of the torque at the electric motor are keptout of the calculation of the control signal for the malfunctionreduction. These portions could possibly evoke imprecision in thedetermination of the output signal. The advantage of this embodiment isa higher level of accuracy in the determination of the control signal ofthe control system.

In a further advantageous embodiment, the control device, the motorcontroller, the converter control system, the high-pass filter and/orthe coupling unit are grouped altogether or in parts to an overallcontrol unit. Since the different control tasks can be established bydifferent software portions on the same hardware unit, this groupingtogether results in a reduction in hardware complexity and thus, inpart, a distinct reduction in costs.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described and explained in greater detailmaking reference to the exemplary embodiments illustrated in thedrawings, in which:

FIG. 1 shows a first block circuit diagram of a system with an electricmotor supplied via a converter, and a control device,

FIG. 2 shows a further block circuit diagram of a system according toFIG. 1, extended with a motor controller and a further input for thecontrol device,

FIG. 3 shows a further block circuit diagram of a system according toFIG. 2, extended with a coupling unit, a high-pass filter and means forfrequency analysis,

FIG. 4 shows a further block circuit diagram of a system according toFIG. 3, wherein parts of the control system are grouped together into anoverall control system, and

FIG. 5 shows an overall block circuit diagram of .a system according tothe invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a first block circuit diagram of a system with an electricmotor 4 supplied via a converter 3, and a control device 1. The maincomponents of the system include a network 2 for the exchange ofelectrical energy, a converter 3 which supplies an electric motor 4, anda control device 1. A converter control system 14 is a functional partof the converter 3. In order to reduce or eliminate malfunctions in thenetwork 2 arising due to torque fluctuations at the electric motor 4, aninput signal 8 is transmitted at an input 7 of the control device 1 withwhich the loading on the network 2 due to torque fluctuations of theelectric motor 4 can be determined. For this purpose, the control device1 generates an output signal 10 at the output 9 of the control device 1which is suitable, with the aid of the converter 3, for counteractingthe malfunctions. This output signal 10 is fed to the converter controlsystem 14 of the converter 3.

FIG. 2 shows a further block circuit diagram of a system according toFIG. 1, extended with a motor controller 5 and a further input 11 forfeeding a further input signal 12 for the control device 1. In thisregard, embodiments can also be realized which comprise only one ofthese two elements as an enhancement. With regard to the othercomponents of the system, reference is made to the description regardingFIG. 1 and the reference signs therein. An input signal 12 whichcontains information on the rotary speed and/or the rotary angle of theelectric motor 4 is fed to the control device 1 at a further input 11.The means 17 for frequency analysis contained in the control device 1can break down the input signal 8 into different frequency components,based on the further input signal 12. The further input signal 12contributes to determining the relevant frequencies for the frequencyanalysis. These are, in particular, the fundamental frequency whichcorresponds to the mechanical motor frequency, and the relevantharmonics. The output 9 of the control device 1 transmits an outputsignal 10 to the converter control system 14 containing only a limitednumber of frequencies. Even with only portions of the fundamentalfrequency, satisfactory control results can be achieved. Each furtherfrequency component improves the control behavior. In this way, theadjustment dynamics are used for the frequencies with which theconverter is able to act most effectively against the malfunction. Themotor controller 5 serves to set the operational working point, forexample, a rotary speed of the electric motor 4. For this purpose, themotor controller 5 requires an input signal 19 from the electric motor4, in this example, a rotary speed signal. As the output signal 16, themotor controller 5 makes a target value available to the converter 3 inorder to regulate the electric motor 4 to the intended working point.

FIG. 3 shows a further block circuit diagram of a system according toFIG. 1 and FIG. 2 so that, for the avoidance of repetition, reference ismade, with regard to matching components of the system, to thedescriptions regarding FIG. 1 and FIG. 2 and the reference signs usedthere. For the further optimization of the regulating behavior, FIG. 3also includes a high-pass filter 15 for processing the input signal 8and a coupling unit 6. In this regard, embodiments can also be realizedwhich comprise one of these two elements as an extension.

The coupling unit 6 links the output signal 10 of the control device 1and the output signal 16 of the motor controller 5 to one another andgenerates an output signal 18 of the coupling unit 6, which istransferred to the converter control system 14 of the converter 3 inorder to control the electric motor 4. The system has the advantage thatthe converter control system 14 must accept only one signal. Anextension to a second input for the converter control system 14 can bedispensed with, so that even existing systems can be enhanced with acontrol device to remedy malfunctions in the network. The high-passfilter 15 serves to process the input signal 8 of the control device 1before the feeding of the signal into the control device 1. Herein, thelow frequency components are removed from the signal. This ensures,inter alia, that control functions of the motor controller, such as theintentional changing of the rotary speed, are not interpreted by thecontrol device 1 as a malfunction. In this way, the interaction ofdifferent control circuits is prevented to the greatest possible extent.The portions causing the malfunctions then remain in the input signal 8.Thus, the determination of the output signal 10 of the control device 1can be carried out more simply, with less effort and more precisely.

FIG. 4 shows a further block circuit diagram of a system according toFIG. 1, FIG. 2 and FIG. 3 so that, for the avoidance of repetition,reference is made in turn, with regard to matching components of thesystem, to the descriptions regarding FIGS. 1 to 3 and the referencesigns used there.

The peculiarity of the exemplary embodiment of FIG. 4 lies therein thatthe regulating components of the system, such as the control device 1,the converter control system 14, the motor controller 5, the high-passfilter 15 and the coupling unit 6 are grouped together into an overallcontrol unit 13. The different components are often only differentsoftware routines which, however, can be executed on the same regulatinghardware. Therefore, different hardware units are not necessarily neededfor the individual regulating components. The assembly of the differentsoftware routines on a hardware unit leads, in many cases, to areduction of costs.

FIG. 5 shows a further exemplary embodiment of a system according to theinvention. A converter 3 connected to the network 2 supplies an electricmotor 4. For regulation of a motor rotary speed, a motor controller 5 isused which as input variables receives, as the actual value, a rotaryspeed signal 101 from the electric motor 4 and as the target value, arotary speed target value 105. Within the motor controller 5, thedifference is formed from the two fed-in values and is passed to arotary speed regulator 108, for example, a PI regulator. The rotaryspeed regulator 108 generates a torque target value 104 which thensimultaneously represents the output signal 16 of the motor controller.As previously shown and described in relation to FIGS. 1 to 4, for thesuppression of the malfunctions in the network 2, in addition to themotor controller 5, a control device 1 is also provided. Frominformation 103 at the electric motor 4, in particular from voltage(s)and current(s), a power signal 112 is generated through means 111 forpower determination. A high-pass filter 15 removes the low-frequencycomponent so that the input signal 8 of the control device 1 receivesonly the power portions giving rise to the malfunctions in the network2. This ensures, inter alia, that control functions of the motorcontroller 5, such as the changing of the rotary speed, are notinterpreted by the control device 1 as a malfunction. In this way, theinteraction of different control circuits is prevented to the greatestpossible extent. Within the control device 1, the input signal 8 is fedto a power oscillation regulator 107. In order to be able to carry out afrequency analysis which relates to the fundamental frequency and theharmonics of the mechanical motor frequency, the mechanical rotor angle102 is formed from the rotary speed signal 101 with the aid of anintegrator 109 and is fed to the means 17 for frequency analysis. Saidmeans generates auxiliary signals 113 for frequency analysis from sineand cosine values of the mechanical rotor angle 102 and its multiples.In principle, any desired number of harmonics can be used for thefrequency-selective regulation. Sufficiently good regulation resultshave been achieved for the fundamental oscillation. FIG. 5 shows theadditional use of the 1st harmonic, which has also proved to be useful.The individual auxiliary signals 113 for frequency analysis aremultiplied in the power oscillation regulator 107, in each case by theinput signal 8, then subsequently integrated, thereafter to bemultiplied by the respective same auxiliary signals 113 for frequencyanalysis, as before. The result is individual additional torque portions115, the total of which is fed to a proportional member 114 whichoptimizes the regulating behavior by means of multiplication by aconstant factor. The resulting output signal is the additional torquetarget value 106 which corresponds to the output signal 10 of thecontrol device 1. The additional torque target value 106 is overlaidnegatively onto the target torque 104 and is fed as the overall targettorque 110 to the converter control system 14.

What is claimed is:
 1. A method for eliminating electrical malfunctionsin a network with a control device, the method comprising: receivingwith a controller of the control device at least one first input signalwhich is formed from a power signal that is generated from informationobtained at an electric motor with a device for power determination,receiving with the controller at least one additional input signalcomprising mechanical information derived from the electric motor,wherein the mechanical information relates to at least one of a rotationspeed and a rotor angle of the electric motor, removing high-frequencycomponents in the at least one first input signal by high-passfiltering, forming from the at least one additional input signalrelating to the rotation speed through integration a mechanical rotorangle, multiplying auxiliary signals formed from sine and cosine valuesof the mechanical rotor angle and its multiples with the at least onehigh-pass-filtered first input signal, integrating the multipliedauxiliary signals and multiplying the integrated multiplied auxiliarysignals again with the auxiliary signals to form additional torqueportions, forming from the additional torque portions an additionaltorque target value, generating with the controller from the additionaltorque target value at least one output signal of the control device,superimposing a negative value of the additional torque target valueonto a target torque to generate an overall target torque, and supplyingthe overall target torque to a converter control system of a converterthat is connected to a network and powers the electric motor.
 2. Themethod of claim 1, further comprising regulating a rotation speed of theelectric motor based on an input signal representing an actual rotaryspeed signal from the electric motor and a target value representing arotary speed target value for the electric motor, and generating as anoutput signal the target torque.
 3. A control device for reducingelectrical malfunctions in a network caused by torque fluctuations of atleast one electric motor, the control device comprising: at least onefirst input for receiving at least one first input signal which isformed from a power signal that is generated from information obtainedat the electric motor with a device for power determination, at leastone additional input for receiving at least one additional input signalcomprising mechanical information derived from the at least one electricmotor, wherein the mechanical information relates to at least one of arotation speed and a rotor angle of the electric motor, and at least oneoutput for outputting an output signal to at least one converterpowering the electric motor for reducing the electrical malfunctions inthe network caused by the torque fluctuations of the electric motor,wherein the control device is configured to remove high-frequencycomponents in the at least one first input signal by high-passfiltering, form from the at least one additional input signal relatingto the rotation speed through integration a mechanical rotor angle,multiply auxiliary signals formed from sine and cosine values of themechanical rotor angle and its multiples with the at least onehigh-pass-filtered first input signal, integrate the multipliedauxiliary signals and multiplying the integrated multiplied auxiliarysignals again with the auxiliary signals to form additional torqueportions, form from the additional torque portions an additional torquetarget value, generate from the additional torque target value at leastone output signal of the control device, superimpose a negative value ofthe additional torque target value onto a target torque to generate anoverall target torque, and supply the overall target torque as theoutput signal to the at least one converter.
 4. A system having at leastone electric motor powered by a converter and at least one controldevice, wherein the control device comprises at least one first inputfor receiving at least one first input signal which is formed from apower signal that is generated from information obtained at the electricmotor with a device for power determination, at least one additionalinput for receiving at least one additional input signal comprisingmechanical information derived from the at least one electric motor,wherein the mechanical information relates to at least one of a rotationspeed and a rotor angle of the electric motor, and at least one outputfor outputting an output signal to at least one converter powering theelectric motor for reducing the electrical malfunctions in the networkcaused by the torque fluctuations of the electric motor, wherein thecontrol device is configured to remove high-frequency components in theat least one first input signal by high-pass filtering, form from the atleast one additional input signal relating to the rotation speed throughintegration a mechanical rotor angle, multiply auxiliary signals formedfrom sine and cosine values of the mechanical rotor angle and itsmultiples with the at least one high-pass-filtered first input signal,integrate the multiplied auxiliary signals and multiplying theintegrated multiplied auxiliary signals again with the auxiliary signalsto form additional torque portions, form from the additional torqueportions an additional torque target value, generate from the additionaltorque target value at least one output signal of the control device,superimpose a negative value of the additional torque target value ontoa target torque to generate an overall target torque, and supply theoverall target torque as the output signal to the at least oneconverter.
 5. The system of claim 4, further comprising at least oneadditional motor controller configured to regulate a rotation speed ofthe at least one electric motor, wherein the additional motor controllerreceives, for regulating the rotation speed of the at least one electricmotor, as an input signal an actual rotary speed signal from the atleast one electric motor and as a target value a rotary speed targetvalue for the at least one electric motor, wherein the additional motorcontroller generates as output signal the target torque.